Excellichlamys spectabilis (Reeve, 1853)

Dijkstra, Henk H. & Beu, Alan G., 2018, Living Scallops of Australia and Adjacent Waters (Mollusca: Bivalvia: Pectinoidea: Propeamussiidae, Cyclochlamydidae and Pectinidae), Records of the Australian Museum (Rec. Aust. Mus.) 70 (2), pp. 113-330 : 190-192

Excellichlamys spectabilis (Reeve, 1853)

Figs 36D,F, 38E–F, 39

Pecten parvus G. B. Sowerby I, 1835: 110 (junior homonym of P. parvus da Costa, 1778); G. B. Sowerby II, 1842: 67, pl. 20, figs 227–228; Reeve, 1853: pl. 29, fig. 133.

Pecten spectabilis Reeve, 1853 : sp. 128, pl. 29, fig. 128; Dunker, 1882: 241, pl. 11, figs 12–13; Küster & Kobelt, 1888: 61, pl. 16, fig. 3.

Pecten histrionicus Gmelin var.–Petit [de la Saussaye], 1853: 150, pl. 5, fig. 2.

Pecten (Aequipecten) histrionicus var. spectabilis Reeve. – Dautzenberg & Bavay, 1912: 22.

Chlamys ( histrionica var.?) spectabilis (Reeve) .–Kuroda, 1932: 95.

Aequipecten histrionicus var. spectabilis (Reeve) .– Lamy, 1935: 314.

Excellichlamys spectabilis (Reeve) .– Iredale, 1939: 366; Kuroda et al., 1971: 366, pl. 79, figs 12–13; Waller, 1972a: 224, 225F, 227, 246–250, 247F, 248T, 25–259, pl. 5, figs 87–92; pl. 6, figs 93–102; Dijkstra, (1983–1994) 1987: 9, figs; Dijkstra, Drivas & Jay, 1998: 7, fig. 8; Dijkstra, 1991: 44; Slack-Smith & Bryce, 2004: 237; Dharma, 2005: 250, pl. 100, fig. 5; Raines & Poppe, 2006: 110–111, lower figs; pl. 55, figs 1–7; Dijkstra & Moolenbeek, 2008: 22; Huber, 2010: 198; Raines, 2010: 606, pl. 994, figs 1–4; Dijkstra, 2013: 38, pl. 8, figs 2a–d, pl. 9, figs 3a–b, pl. 26, figs 2a–b.

Semipallium (Excellichlamys) xishaensis Wang, 1985: 504 , figs 4a–d.

Semipallium spectabilis (Reeve) .–Wells & Slack-Smith, 1986: 54.

Excellichlamys spectabilis parva (Sowerby I) .–Dijkstra, 1989: 2 (colour fig.), 14 (fig.), 15, 18.

Excellichlamys sowerbyi Dijkstra, 1998b: 247 (replacement name for P. parvus Sowerby ).

Excellichlamys histrionica (Gmelin) .–Xu & Zhang, 2008: 89, fig. 252 (misidentification).

Type data. Pecten parvus Sowerby : holotype (pr) NHMUK197011 , refigured by Waller (1972a: pl. 6, figs 97–102). Type locality: French Polynesia, Tuamotu Archipelago , Actaeon Group, Lord Hood’s Island (now Marutea), in coral sand on the reefs.

Pecten spectabilis Reeve : holotype (pr) UMZC.1461 (Jane Saul collection). Type locality unknown.

Semipallium (Excellichlamys) xishaensis Wang : holotype (pr) IOAS M25777. Type locality: China, South China Sea, Xishi Islands , Jinqing Island , intertidal, leg. F. Xu, 1 May 1958.

Comments on type data. A sample consisting of three articulated specimens ( NHMUK, not registered) from Mauritius is similar to the holotype of Pecten spectabilis and could have come from the same lot as the Saul collection. According to labels written by S. Morris, these specimens have no type status .

Additional material examined. — AUSTRALIA: QUEENSLAND: Lizard Island, Casuarina Beach , 14°67' S 145°45'E, dead (2 v, ZMA Moll.142904); Townsville, “ Yongala ” wreck, 19°24'S 146°82' E, alive, 27 m (1 pr, photo T. C. Good, AM). WESTERN AUSTRALIA: Dampier Archipelago, Rosemary Island, Norbay, 20°31'S 116°35'E, dead, beach (1 v, WAM); Dampier Archipelago, NE side of Rosemary Island, Lady Dora Flats, approx. 20°29'S 116°35'E, alive (1 pr, WAM); DampierArchipelago,Kendrew Island, 20°28.30'S 116°32'E,dead (1 v,WAM);Dampier Archipelago, Kendrew Island, N of Citadel, 20°28.30' S 116°32'E, dead (1 v, WAM); Rowley Shoals, Clerke Reef, approx. 17°10'S 119°20'E, dead, 9–18 m (1 v, WAM 1621.82); Kimberley, Doubtful Bay, Raft Point, 16°04' S 124°27'E, dead (1 v, WAM); Kimberley, Gibbings Reef, 15°56.05' S 123°46.05'E, dead (2 v, WAM); Kimberley, Macleay Island, 15°56.02' S 123°62.03' E, on reef,dead (1 v,WAM);Kimberley,Macleay Island, 15°56.02'S 123°42.03'E,dead, 30 m (10 v,WAM);Kimberley, E of Wilson Point, 15°33' S 124°25'E, dead,beach (1 v, WAM);Churchill Reef, 15°31'S 123°17'E, dead (1 v, WAM); Kimberley, Lucas Island, SW corner, 15°13'S 124°31'E, dead (1 v, WAM); Kimberley, Rob Roy Reef, 14°51.09'S 124°25.06'E, alive (1 pr, WAM); Kimberley, Wollaston Island, 14°29'S 125°30'E, dead (1 v, WAM); Descartes Island, 14°11'S 125°38' E,dead (1 v,WAM);Kimberley,W side of Long Reef, 13°58' S 125°38'E,dead (1 v,WAM);Kimberley, E of Montalivet Island,dead (1 v,WAM);Cassini Island, 13°56'S 125°38'E,dead (5 v,WAM);Cassini Island, 13°56'S 125°38' E, dead, 20 m (3 v,WAM); Cassini Island, 13°56'S 125°38'E,dead, 20–25 m (11 v,WAM);Ashmore Reef,NE corner, 12°17'S 123°02'E, dead, 20–25 m (1 v,WAM);Hibernia Reef, 11°58'S 123°19'E,dead, 5 m (1 v, WAM). —RED SEA: Gulf of Aqaba, S of Elat, alive, 10–15 m (2 pr, ZMA Moll.142901).— MAURITIUS:alive, 32 m (1 pr, ZMA Moll.142910). — REUNION: Boucan-Canot, alive, 34 m (1 pr, ZMA Moll.142913). — THAILAND: Phuket Island, alive, 4–8 m (1 pr, ZMA Moll.140284); S Phuket Island,Kho Raya Ya, alive, 25–40 m (2 pr, ZMA Moll.143687);off Pangga, alive, 73 m (1 pr, ZMA Moll.140843).— JAPAN: Okinawa,Seragaki, alive, 38–43 m (1 pr, ZMA Moll.141431). HONG KONG: E Peng Chou, dead, 3 m (1 v, ZMA Moll.140541). — PHILIPPINE ISLANDS : Cebu, Mactan, Magellan Bay, alive, 120–180 m (2 pr, ZMA Moll.145520); Davao, Talikud Island, alive, 80–200 m (1 pr, ZMA Moll.144234). GUAM: off Orote Cliffs, alive, 21–25 m (5 pr, ZMA Moll.142918).— MARSHALL ISLANDS : Kwajalein Island,alive, 6 m (1 pr, ZMA Moll.142933); Majuro Atoll,alive, 2–5 m (1 pr, ZMA Moll.139736).CORAL SEA: North East Herald Cay, 16°56'S 149°11'E, dead, beach (8 v, C.331904).— NEW CALEDONIA: Nouméa, Channel Ilot Maître, alive, 20 m (1 pr, ZMA Moll.141322); Baie de Citron, alive, 1 m (1 pr, ZMA Moll.141454). — PAPUA NEW GUINEA: off Port Moresby, alive, 1–2 m (2 pr, ZMA Moll.142914). — SOLOMON ISLANDS : W Honiara, alive, 26–32 m (4 pr, ZMA Moll.142909); Russell Group, Pavuvu Island, Samata, alive, 6–12 m (1 pr, ZMA Moll.142907). — FIJI ISLANDS : Viti Levu, Beqa Island, alive, 9 m (2 pr, ZMA Moll.142930). — SAMOA ISLANDS : Tutuila Island, Fagasy Bay, dead, 22 m (1 pr, ZMA Moll. 142932). —LINE ISLANDS : Christmas Island, Bay of Wrecks,alive, 10–18 m (1 pr, ZMA Moll.142925);Cook Isle,alive, 12 m (1 pr + 1 v, ZMA Moll.142927).—SOCIETY ISLANDS :Tahiti,alive, 32 m (1 pr, ZMA Moll.144604).—TUAMOTU ISLANDS :Hao Island, alive (1 pr, ZMA Moll.144615).

Description. Shell up to c. 30 mm high, most specimens to about 20 mm; solid, circular to slightly oblong, inequivalve, right valve more convex than left, equilateral, auricles unequal to almost equal in size, umbonal angle c. 90°; plicae unpigmented or pinkish, with brown maculations, interspaces paler, umbones tinted red; many specimens with prominent pink and brown maculations on alternate plicae; right valve paler; interior white.

Both valves sculptured with c. 12 variable high plicae with rounded crests, bearing strongly developed recurved squamae; radial grooves with intercalated radial riblets commencing at about 10 mm shell height, increasing in prominence to ventral margin, subdividing plicae into bifid or trifid groups after about 20 mm shell height. Microsculpture of closely spaced commarginal lamellae on plicae and interspaces, weak on anterior auricle of left valve. Auricles with 4–10 radial costae (anterior 4–9, posterior 4–10), more prominent on dorsal areas than on lower areas of auricles near disc, crossed by prominent commarginal folds. Byssal notch

Figure 38. A, C, Decatopecten radula (Linnaeus) , specimen in Fig.36A, C; lv exterior (A), rv interior (C).B, D, H, J, Glorichlamys quadrilirata (Lischke) (B, D) specimen in Fig. 36B, E; rv interior (B), lv exterior (D); (H, J) pair, NTM P018368, Mandorah jetty, Cox Peninsula, W side Darwin Harbour, NT, 12°26.584'S 130°46.088'E, 9 m; lv exterior (H), rv interior (J). E, F, Excellichlamys spectabilis (Reeve) , specimen in Fig. 36D, F; lv exterior (E), rv interior (F). G, I, Glorichlamys elegantissima (Deshayes) , specimen in Fig. 36G–I; lv exterior (G), rv interior (I). Scale bars represent 50 mm (A, C), 10 mm (B, E, G–J), 20 mm (E, F).

Figure 39. Distribution of Excellichlamys spectabilis (Reeve) (circles), Glorichlamys elegantissima (Deshayes) (stars) and G. quadrilirata (Lischke) (triangles).

moderately deep, byssal fasciole rather wide, functional ctenolium with 3–5 teeth. Hinge teeth very weak or lacking. Hinge surface with minute, irregularly formed, transverse grooves. Internal plicae with carinate edges near margin.

Dimensions. Illustrated specimen: WA, N end of Flying Foam Passage, Dampier Archipelago, MV Davena (WAM S43979 ): H 30.7, L 32.5 mm.

Habitat. Living in the intertidal zone and on the continental shelf, byssally attached to undersides of coral slabs or amongst coral rubble on soft sediment (sand or muddy sand).

Distribution. Throughout the tropical Indo-West Pacific, from southern Japan to northern Australia, westwards into the Indian Ocean to Mauritius and Réunon, and eastwards across the central Pacific to the Tuamotu Archipelago. Red Sea, 4–15 m (Dijkstra & Knudsen, 1998: 58); Mauritius; Japan, 18 m; Philippines, 18–83 m (dead); Indonesia, Papua, 25–45 m; New Caledonia, 0.3–1.5 m; Fiji Islands ; Palau Islands , 1-6 m; Marshall Islands ; Tuamotu Archipelago (Waller, 1972: 249–250). Philippines, 19–90 m (Dijkstra, 2013: 38); Indonesia, 6–57 m (Dijkstra, 1991: 44); Papua New Guinea, 10–52 m (Dijkstra, 1998a: 20). Maximum depth range of live-taken specimens from the intertidal zone to c. 200 m. Present specimens from Australia alive at 27 m, dead at 5– 30 m.

Remarks. Iredale (1939: 366) mentioned this species from the Great Barrier Reef, but did not specify the locality. Cotton (1964: 10) listed a valve from Yirrkalla (NT). However, no live records are known from that region. The present material from Queensland and Western Australia resembles the holotype, although the auricles of Australian specimens are more unequal (typically almost equal in size) and they have more prominent intercostal radial riblets (typically almost without secondary riblets). Auricles and secondary interstitial radial riblets are highly variable in this species and intermediate variants are also observed.

Wang (1985: 504) described a species from Jinqing Island ( China), Semipallium (Excellichlamys) xishaensis , which resembles E. spectabilis but has strongly unequal auricles (the posterior ones are rudimentary) and fewer primary radial plicae. This form is identical to the French Polynesian morph, Pecten parvus G. B. Sowerby I, 1835 (preoccupied by Da Costa (1778: 153), renamed by Dijkstra (1998b: 247) as Excellichlamys sowerbyi .

The tropical western Pacific species Excellichlamys histrionica (Gmelin, 1791) differs from E. spectabilis in lacking costae in the interspaces between plicae or in developing them weakly in the late growth stage. The plicae of most specimens are narrower and of even amplitude, and the interspaces are broader than in E. spectabilis .